Earpiece



y 1939- N. A KURMAN 2,156,632

EARPIEGE Filed Oct. 27, 1937 Hem.

3| lNVENTO R 4 1 NATHAN A. KURMAN l2 34 k vqzmulwm ATTORNEY Patented May 2, 1939 EARPIECE Nathan A. Kurman, Woodside, I Application October 27, 1937, Serial N0.Y 17/1,239'

1 Claim.

This invention relates to an electro-magnetic earpiece suitable for use by partially deaf persons.

An object of the invention is the provision of a highly efficient earpiece so compact that it may be retained within the outer ear of the user and which at the same time has a highly efficient electro-magnetic structure.

A further object is the provision of a novel method of supporting the polepiece which enables the device to be made cheaply in quantity production.

Other objects will appear in the following description, given with the aid of the accompanying drawing, of which Figure 1 is a sectional view of a receiver cap retaining ring. This figure as well as the other figures in the case are considerably enlarged for the sake of clearness.

Figure 2 is a sectional view of a receiver cap;

Figure 3 is an edgewise view of a diaphragm;

Figure 4 is a section of the receiver shell;

Figure 5 is a section taken through 5-5 of Figure 6;

Figure 6 is a top view;

Figure 7 is a top view of the shell p;

Figure 8 is a side view;

Figure 9 is a top view of the receiver shell, similar to Figure '7, except that the cord connections are not shown;

Figure 10- is an enlarged view of a bent polepiece;

Figure 11 is a laminated E-shaped polepiece;

Figure 12 of an E-shaped polepiece and retaining strip.

Referring to Figures 4 and 5 of the drawing which show the earpiece as consisting of a receiver shell I, having 'a thickened base and side section into which is molded a U-shaped magnet 2 having poles 3 and 4. Prior to the molding operation a strip of Bakelite, i. e., a resinous productof the phenolformaldehyde condensation product type, is placed between the poles in the manner shown in the drawing to act as a support for the magnet yoke.

Pole piece 4 is thrust through form-wound coil 6 which is retained in place by friction, and the terminals of the windings are soldered to spring clips 1 and 8, secured by rivets 9 molded into the wall of the receiver shell.

A pointed stud I!) is fastened to the end of each spring clip, the points H thereof extending respectively into openings l3 and It in a reinforced part It of the shell, forming a flange 22.

A retaining ring 20, threaded to screw over without the corresponding threads on the outside of the receiver shell is formed with a turned over part 2!, leaving a circular opening of sufilcient size to slip over 9 and engage shoulder 22, so that when the parts arein place the cap may be rotated in respect to cord tips It and locked at any desired position by ring'20.

A hollow'nipple-shaped piece 23, of a size and shape adapted to fit into the inner ear is thread ed at 24 and screwed into opening 25 in a slanting projection at the top of the'receiver cap.

In order to form an efiicient magnetic circuit, the polepiece of the magnet is made from a highly permeable nickel-iron alloy, such as Permalloy. This metal must be heat treated after machining or being subjected to strain, in order to get full advantage of its magnetic properties.

Formerly, it was customary in receivers of this kind, to so arrange the polepiece within the molds so that the ends thereof be in approximate alignment with the platform on which the diaphragm rests, the polepiece being supported at or near the tips. In production this method was found to be injurious to the magnetic properties of the polepiece, because of the pressure exerted thereon by thethermoplastic material of which the shell was made, since it became plastic only under heat and pressure. During the molding operation, polepieces often became deformed as shown in Figure 10. Such deformation destroyed the magnetic virtue of the metal used, which was established in that material by a careful process of heat treatment.

Furthermore, due to the necessarily small size of the earpiece, the structure did not lend itself to the use of conventional methods for anchoring the polepiece in the base, consequently, there was a tendency for the polepiece to adhere to the mold on withdrawal, producing in such cases a small air space in the plastic material about the yoke which could not be discovered easily since the lower part or the polepiece was entirely covered with plastic material. This resulted in a more or less weakened structure.

By means of the present invention, mutilation of the polepiece during the molding operation is prevented, and a secure anchorage for the polepiece is provided. Furthermore, the speed of pro-, duction is increased, for the shells may be r moved more quickly from the mold than was possible in the case of former methods.

The U-shaped polepiece 2 is inverted on a supporting member in a mold on which rests a strip of canvas Bakelite, i. e., canvas impregnated with Bakelite and treated and hardened so that the strength of the canvas is imparted to relatively thin sheets of Bakelite, 5, the ends l2 of which extend a short distance beyond the edge of the polepiece on each side. The strip 5 is punched with a punch smaller than the die for the purpose of producing a rather rough, serrated edge on the piece.

The mold is so shaped that the plastic material is formed along the edges and outside face of one polepiece 3 for the greater part of its length, as well as enclosing a substantial part of the piece 5 where it extends beyond the polepiece. An irregular depression having a flat base of which the Bakelite strip is part, is formed about the partially unsupported polepiece 4 to provide a space for the form wound coil 6.

The plastic material coheres with strip 5 during the molding operation and becomes part thereof, and thus the polepiece is secured in a unitary structure, the previously prepared strip 5 presenting a large flat surface deeply imbedded in the shell material and is more than sufiicient to retain the polepiece firmly in place on removal from the mold, even in the event that the shell might not be completely hardened.

Figures 11 and 12 show the invention as applied to an E-shaped polepiece. Individual retaining strips similar to 5 in Figure 4 may be inserted between the polepieces, but a preferred arrangement is to use a strip having an opening in the center which closely fits the middle polepiece.

Figure 12 shows an E-shaped polepiece made up of two U-shaped sections having outer poles 3| and 32 and a middle pole 33, the sections being held together by a retaining strip 34 having an opening 35 closely fitting over the middle pole and forming an assembly which may be molded into a shell in the manner previously described in connection with the U-shaped polepiece.

Figure 11 shows a polepiece formed of E- shaped laminations which are held together prior to the molding operation, and supported to prevent distortion during the molding operation by a retaining strip of suitable material, 34.

What is claimed is:

The method of securing during a molding operation a U-shaped magnet in a miniature receiver shell which comprises placing a substantially rigid strip of insulating material between the poles of said magnet at the yoke thereof, and thereafter injecting into a mold in which said magnet and said strip are positioned, plastic material so that it envelops the greater part of one polepiece as well as the sides of said strip.

NATHAN A. KURMAN. 

